1. Field of the Invention
This invention relates to novel heterocyclic compounds and methods for their preparation and is more particularly concerned with compounds which contain both an anhydride group and a hetero ring which can dissociate on heating to yield an isocyanate group, and with polymers derived from said compounds by self-condensation and or by copolymerization in the presence of additional polyfunctional monomers.
2. Description of the Prior Art
Various types of compounds have been described which can undergo self-condensation to generate polymers. Illustratively, U.S. Pat. No. 3,951,922 describes isocyanato-phthalic anhydrides which, upon heating, undergo self-condensation to form polyimides. The conversion of caprolactam to polyamides is, of course, a well-recognized and widely practiced commercial process which involves generation of a polymer from a single monomer and can be broadly regarded as self-condensation.
A somewhat related process is that described in U.S. Pat. No. 4,138,398 in which certain bis(cyclic ureas) are utilized as blocked isocyanates insofar as they undergo ring-opening to form diisocyanates upon heating. By heating a mixture of stoichiometric amounts of these bis(cyclic ureas) and an appropriate polyol, which mixture is stable upon storage until utilized, it is possible to prepare polyurethanes.
I have now found a novel class of compounds which contain, in the same molecule, a dicarboxylic acid anhydride group and a hetero ring (cyclic urea) which will undergo ring opening to yield an isocyanato group upon heating to the appropriate temperature. This combination of groups in the same molecule enables the compounds in question to undergo self-condensation upon heating. It also enables the production of a considerable range of novel copolymers by conducting the self-condensation reaction in the presence of difunctional or polyfunctional monomers which contain groups reactive with either isocyanato groups or dicarboxylic acid anhydride groups or both.